Mammalian phosphomannomutase PMM1 is the brain IMP-sensitive glucose-1,6-bisphosphatase.
Glucose 1,6-bisphosphate (Glc-1,6-P(2)) concentration in brain is much higher than what is required for the functioning of phosphoglucomutase, suggesting that this compound has a role other than as a cofactor of phosphomutases. In cell-free systems, Glc-1,6-P(2) is formed from 1,3-bisphosphoglycerate and Glc-6-P by two related enzymes: PGM2L1 (phosphoglucomutase 2-like 1) and, to a lesser extent, PGM2 (phosphoglucomutase 2). It is hydrolyzed by the IMP-stimulated brain Glc-1,6-bisphosphatase of still unknown identity. Our aim was to test whether Glc-1,6-bisphosphatase corresponds to the phosphomannomutase PMM1, an enzyme of mysterious physiological function sharing several properties with Glc-1,6-bisphosphatase. We show that IMP, but not other nucleotides, stimulated by >100-fold (K(a) approximately 20 mum) the intrinsic Glc-1,6-bisphosphatase activity of recombinant PMM1 while inhibiting its phosphoglucomutase activity. No such effects were observed with PMM2, an enzyme paralogous to PMM1 that physiologically acts as a phosphomannomutase in mammals. Transfection of HEK293T cells with PGM2L1, but not the related enzyme PGM2, caused an approximately 20-fold increase in the concentration of Glc-1,6-P(2). Transfection with PMM1 caused a profound decrease (>5-fold) in Glc-1,6-P(2) in cells that were or were not cotransfected with PGM2L1. Furthermore, the concentration of Glc-1,6-P(2) in wild-type mouse brain decreased with time after ischemia, whereas it did not change in PMM1-deficient mouse brain. Taken together, these data show that PMM1 corresponds to the IMP-stimulated Glc-1,6-bisphosphatase and that this enzyme is responsible for the degradation of Glc-1,6-P(2) in brain. In addition, the role of PGM2L1 as the enzyme responsible for the synthesis of the elevated concentrations of Glc-1,6-P(2) in brain is established.
Veiga-da-Cunha
Maria
M
Laboratory of Physiological Chemistry, de Duve Institute, Université Catholique de Louvain, Avenue Hippocrate 75, B-1200 Brussels, Belgium. maria.veiga@uclouvain.be
Vleugels
Wendy
W
Maliekal
Pushpa
P
Matthijs
Gert
G
Van Schaftingen
Emile
E
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002460:Cell Line; D005947:Glucose / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007291:Inosine Monophosphate / Q000737:chemistry*; D007700:Kinetics; D051379:Mice; D009711:Nucleotides / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry*; D017875:Phosphotransferases (Phosphomutases) / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D014018:Tissue Distribution
D009711:Nucleotides; D011994:Recombinant Proteins; D007291:Inosine Monophosphate; C014818:glucose 1,6-diphosphate phosphatase; D010744:Phosphoric Monoester Hydrolases; D017875:Phosphotransferases (Phosphomutases); C052799:phosphomannomutase; D005947:Glucose